The present invention relates to a portable telephone terminal and, more particularly, to a portable telephone terminal or other types of portable terminals which can change their shapes by stretching or folding their housings. The present invention can also be applied to a circuit which provides input impedance matching for an antenna in accordance with a change in the input impedance of the antenna when the shape of a housing is changed.
In a portable telephone terminal, in order to optimize the radiation efficiency of an antenna, an impedance matching circuit is arranged between the antenna and a transmission/reception radio circuit. This impedance matching circuit provides impedance matching.
The shape of the housing of a folding portable telephone terminal changes as it is folded or unfolded, and hence the input impedance of the antenna changes. For this reason, in a folding telephone terminal, impedance mismatching occurs between the antenna and the transmission/reception radio circuit between when the terminal is folded (e.g., the incoming wait state) and when the terminal is unfolded (e.g., the speech communication or operation state), resulting in deterioration in antenna efficiency.
In order to cope with such impedance mismatching that occurs when the shape of the housing of a folding portable terminal changes, an arrangement has been proposed (e.g., Japanese Patent Laid-Open No. 2001-345882), in which a plurality of impedance matching circuits are prepared, and whether or not the portable terminal is folded is detected. In this arrangement, the impedance matching circuits are selected and switched depending on whether the terminal is folded or unfolded (open).
In the portable terminal disclosed in Japanese Patent Laid-Open No. 2001-345882, two matching circuits having different circuit constants are prepared in advance. These two matching circuits are selected and switched in accordance with a detection result on the open/closed state of the folding portable terminal. This portable terminal is based on the premise that two matching circuits are mounted in advance. Since the portable terminal requires a plurality of circuits with circuit constants corresponding to different impedances, the degree of freedom in design is low. For example, preparing many matching circuits will interfere with a reduction in circuit size.